Rice straw and bagasse with water content 84 or 94% were irradiated with microwave (2450MHz) in sealed glass vessels. This treatment enhanced markedly the accessibility of the cellulosic materials for the enzymatic hydrolysis: for example, 1.6 times in the rice straw by the microwave treatment at 170 °C for 5 min and 3.2 times in the bagasse by the treatment at 200 °C for 5 min, compared with the untreated.